[mojo-edk] Support transferring null Mach ports.

mojo/edk/system/channel.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_EDK_SYSTEM_CHANNEL_H_
 #define MOJO_EDK_SYSTEM_CHANNEL_H_
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ skipping 58 matching lines @@
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
     struct MachPortsEntry {
       uint16_t index;
       uint32_t mach_port;
       static_assert(sizeof(mach_port_t) <= sizeof(uint32_t),
                     "mach_port_t must be no larger than uint32_t");
     };
     static_assert(sizeof(MachPortsEntry) == 6,
                   "sizeof(MachPortsEntry) must be 6 bytes");
+
+    struct MachPortsExtraHeader {
+      uint16_t num_ports;
+      MachPortsEntry entries[0];
+    };
+    static_assert(sizeof(MachPortsExtraHeader) == 2,
+                  "sizeof(MachPortsExtraHeader) must be 2 bytes");
 #endif
 #pragma pack(pop)
 
     // Allocates and owns a buffer for message data with enough capacity for
     // |payload_size| bytes plus a header, plus |max_handles| platform handles.
     Message(size_t payload_size,
             size_t max_handles,
             Header::MessageType message_type = Header::MessageType::NORMAL);
 
     ~Message();
@@ skipping 59 matching lines @@
 
 #if defined(OS_WIN)
     // On Windows, handles are serialised into the extra header section.
     PlatformHandle* handles_ = nullptr;
 #else
     ScopedPlatformHandleVectorPtr handle_vector_;
 #endif
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
     // On OSX, handles are serialised into the extra header section.
-    MachPortsEntry* mach_ports_ = nullptr;
+    MachPortsExtraHeader* mach_ports_header_ = nullptr;
 #endif
 
     DISALLOW_COPY_AND_ASSIGN(Message);
   };
 
   // Delegate methods are called from the I/O task runner with which the Channel
   // was created (see Channel::Create).
   class Delegate {
    public:
     virtual ~Delegate() {}
@@ skipping 83 matching lines @@
   Delegate* delegate_;
   const scoped_ptr<ReadBuffer> read_buffer_;
 
   DISALLOW_COPY_AND_ASSIGN(Channel);
 };
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_CHANNEL_H_